Fix race in ThreadsManager::sleep()

We cannot set do_sleep flag of main thread before
"bestmove" is sent to GUI, otherwise GUI could send
immediately the next "go" command that triggers
start_thinking() and because do_sleep is set UI
thread resets the flag to launch a new search. But
when shortly after main thread returns to main_loop()
flag is incorrectly reset and main thread goes to sleep
hanging the engine.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

diff --git a/src/thread.cpp b/src/thread.cpp
index d67b9fcdef16ba6f5cd0f40c3bb7bb33078665d6..ab20d781796a7b602e3048431447ad409ce7041b 100644 (file)
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -227,7 +227,7 @@ void ThreadsManager::read_uci_options() {
 
 void ThreadsManager::wake_up() {
 
 
 void ThreadsManager::wake_up() {
 

-  for (int i = 0; i < size(); i++)
+  for (int i = 1; i < size(); i++) // Main thread is already running

   {
       threads[i]->do_sleep = false;
 
   {
       threads[i]->do_sleep = false;
 


@@ -237,12 +237,13 @@ void ThreadsManager::wake_up() {
 }
 
 
 }
 
 

-// sleep() is called after the search to ask threads to wait on sleep condition
+// sleep() is called after the search to ask all the threads but the main to go
+// waiting on a sleep condition.

 
 void ThreadsManager::sleep() {
 
 
 void ThreadsManager::sleep() {
 

-  for (int i = 0; i < size(); i++)
-      threads[i]->do_sleep = true;
+  for (int i = 1; i < size(); i++) // Main thread will go to sleep by itself
+      threads[i]->do_sleep = true; // to avoid a race with start_thinking()

 }
 
 
 }